In the selection of degassing agent need to choose according to the specific application of the system, such as yellow high requirements to minimize the use amount of benzoic, and for degassing agent containing wax also need to consider the negative effects of excessive import from the general strength of the manufacturers will give out the corresponding application instruction.
Two, the application of light stabilizers and antioxidants in powder coatingsPowder coating by high temperature baking or sun exposure will occur after aging, yellowing phenomenon has seriously affected the appearance and performance of our products demand, in order to prevent or reduce the occurrence of this trend, we usually use the addition of antioxidant or light stabilizers to realize, although there are many factors affecting the film aging, such as resin, pigments, additives, coating quality and type of formulation design, production process, the change of temperature and the composition of the atmosphere, humidity and other natural factors, but the application of suitable additives is to reduce the occurrence of this trend.
The aging mechanism of polymer is described in detail in the chapter of "outdoor powder coating crosslinking agent and its application". In fact, is a kind of antioxidant to inhibit or delay the oxidation and degradation of polymer material. Many varieties of antioxidant effect, are not the same, if according to the mechanism of classification it can be divided into two categories, a class called chain-breaking antioxidant, the emergence of such antioxidants and free radicals in the polymer chain reaction interrupted growth also known as primary antioxidants, another class called preventive antioxidant, this kind of antioxidants can generate free radicals and inhibit or slow initiation process, also known as auxiliary antioxidant. The Lord has hindered phenolic antioxidant, secondary aromatic amine, a preventive antioxidant phosphite, two dithiocarbamate metal salts, so in the practical application of how to select antioxidants?
Colour change. Discoloration problem antioxidant is one of the important factors we consider. General phenolic antioxidants no pollution, can be used for colorless or light color system and the discoloration of aromatic amine and strong pollution.
Volatile. High molecular weight antioxidants for low volatile, different varieties of antioxidants also have great differences. Therefore, the choice should be based on the selection of different varieties.
Solubility. The ideal antioxidant is high solubility in polymer solubility in Yan in other medium and low factors depending on the structure and types of antioxidants and temperature etc..
The structure of the polymer. It is necessary to point out that different polymer structures have different antioxidant capacity in antioxidant must take into account the differences.
The effect of heat. The effect of heat is extremely important, and the temperature increases about 10 times per hour. At 100 C, the oxidation rate will be about 256 times higher than that at room temperature (20 degrees C). Oxidation at high temperature is a very important factor. Must choose the high temperature performance good antioxidant. Hindered phenolic antioxidants in the high temperature performance is poor, and the two kind is acridine tetrahydroquinoline special use value at high temperature.
The effect of metal ions. Multivalent metal ions such as copper, iron, manganese and other trace elements will accelerate the oxidation of the polymer, so the metal ion deactivators to resist.
Such as N- and salicylic -N '- salicylhydrazone is an inhibitor of copper.
-C – NH – N = C-
The coordination effect. Amine or phenolic antioxidant chain termination and peroxide decomposition agent (e.g. phosphite ester) with the use of polymer can improve the ability of anti oxidation, which is also known as the coordination effect. The coordination effect refers to two or more than two kinds of antioxidants with various effects when using sum total effect is greater than when used alone. But when using several antioxidants also may have a harmful effect, also known as the antagonistic effect of antioxidants, antioxidant effect should be considered when coordination should also consider the antagonistic effect.
The use of antioxidants. The amount of antioxidants depends on the type of polymer. Factors of crosslinking system and antioxidant efficiency, synergistic effect and cost etc.. Most antioxidants have a suitable concentration at an appropriate concentration within the increasing amount of antioxidant capacity increased more than appropriate concentration has adverse effects, should also be considered antioxidant evaporation, extraction, oxidation loss and other factors.
2.UV absorbent and light stabilizer
Ultraviolet absorber (UV absorber) is a type of stable AIDS prevention, in the ultraviolet selectively, endanger the polymer structure before strongly absorb ultraviolet light, and convert them into harmless low-energy radiation, prevent the UV irradiation of polymers.
The photophysical process typical UV absorber is formed by intramolecular hydrogen bond chelate ring to absorb energy photons inhaled off hydrogen bond chelate ring in this process, the light energy is converted to heat release. The stronger hydrogen bond is formed in the UV absorber, the higher the cracking energy of the bond, the more energy it can absorb ultraviolet radiation. The protective effect of ultraviolet absorber depends on the thickness of the coating film is protected, according to Lambert. Bill's Law: E (lambda) = epsilon (lambda) C.D.
ε -The molar absorption wavelength
C - UV absorber concentration
D - film thickness
E - absorbance at lambda wavelength
The same kind of ultraviolet absorber in different concentrations, film thickness, the ability to absorb ultraviolet radiation is also different, the thicker the film, the better the effect of UV absorbers. There are two commonly used UV absorbent benzophenone compounds, benzene and three azole compounds (such as Tinuvin 900).
HALS is a free agent acquisition agent, mainly including piperidine, imidazolidine ketones, Azacycloalkane ketone derivatives, in photooxidation of polymer materials in these compounds by capturing free radicals, decomposition of hydrogen peroxide and quenching of excited state energy to achieve the purpose of anti aging, commonly used in nonferrous system, such as icba-Gergy Tinuvin144 is a kind of material.
The mechanism of light stabilizer with the use of the excellent results are obtained both in plastic, paint, if it can capture free radicals ability of hindered amine light stabilizers (HALS) and with UV absorber can get light stabilization effect is very good, the same HALS antioxidant and phosphite mixed use and its effect synergistic effect.
Charge regulator series
Charge regulator series we simply put them into the friction agent and charge control agent in two parts, the first to talk about the charge control agent, adding antistatic agent or charge regulator in powder coatings can reduce the surface resistance of the powder is deposited on the surface of the powder to work better, but also improved the electrostatic spraying method Ladi effect. As far as electrostatic coating is concerned, a very strong voltage is applied between the workpiece and the electrode of the spray gun and a strong electrostatic field is generated. Due to the applied voltage is high enough to produce CORONA discharge in part gunpoints, CORONA plasma discharge is a cold, it will produce a large number of electrons in the discharge region and is filled between the electrode and the workpiece, these electrons can produce adsorption of negatively charged ions in the air molecules, adsorbed on the powder particles and with the process of spraying deposition in the workpiece on the charged ions will be charged, in fact the efficiency of the powder particles is very low, only about 0.5%, most of the other free ions, they will be as the spraying process adsorbed on the coated surface and accumulated until rejection or discharge, seriously affecting the rate of powder deposition and further the groove on the surface of the powder, and the surface charge regulator can improve balance or by accumulation of free ions coated on the surface of the workpiece, thereby improving the spraying effect, so thick Film coating has also become possible.
The high surface resistance of the polymer surface makes it difficult to discharge the static charge, which can be obtained by.
Increasing the humidity of the processing environment is conducive to the suppression of static charge and the leakage of the charge;
To improve the structure of polymers, such as the introduction of polar or ionic groups to improve the conductivity;
The addition of conductive materials such as metal powder in polymer materials, such as carbon black;
Adding antistatic agent to improve material polarity or hygroscopicity.
The characteristics of the above methods, the moisture on the surface resistance material or volume resistance has great influence, and some methods such as adding metal powder or improving polymer materials not in any applications can be easily obtained, there are limitations, and method of adding antistatic agent of the most simple.
The antistatic agent can be divided into ionic and non-ionic form according to whether it can be ionized. If the hydrophilic ionization is negatively charged anionic, cationic and charged for. If a hydrophilic group of more than two and the ionization after each with different charge is divided into zwitterionic antistatic agent, if not ionization is known as non-ionic antistatic agent, regardless of how the classification of its principle is basically the same, mainly using the surface active characteristics of absorbing moisture in the air, the surfactant has a conductive layer formed of thin polarization, a charge leakage channel. Therefore, most of the antistatic effect depends on the relative humidity of the structure and environment. Compared with the mechanism of moisture absorption, the effect of adding the antistatic agent and reducing the friction coefficient to a certain extent also restrain the generation of electrostatic charge. It should be noted that the amount of antistatic agent and polymer structure and the use of the environment, too much import will lead to the reduction of spray efficiency and even the phenomenon of non adsorption.